Expander XL state machine question

Elliott, Robert (Server Storage) elliott at hp.com
Thu Feb 24 11:21:04 PST 2005


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <elliott at hp.com>
*
An expander is expected to insert ALIGNs on underflows (see section 7.3
on "clock skew management") during a connection.  It doesn't care about
the type of connection or what is going on in the connection.

--
Rob Elliott, elliott at hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology
https://ecardfile.com/id/RobElliott


 

> -----Original Message-----
> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf 
> Of Fred Dutton
> Sent: Thursday, February 24, 2005 12:09 PM
> To: t10 at t10.org
> Subject: Expander XL state machine question
> 
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Fred Dutton <fred.dutton at qlogic.com>
> *
> 
> While in the XL7:Connected state, an expander PHY is required 
> to send Transmit Dword messages to the XL 
> transmitter to transmit all dwords received with Forward 
> Dword indications.
> 
> What type of message should be sent to the XL transmitter 
> when there are no Forward Dword indications? 
> This can occur because devices may run at slightly different 
> clock rates. So if an expander is running 
> faster than an end device or any other device connected to 
> it, it will, every now and then, end up with a 
> "dword bubble" in the transfer and, hence, no Forward Dword 
> indication.
> 
> If the XL state machine sends Transmit Idle Dword messages 
> you run the risk of inserting an idle dword in 
> the middle of a data frame currently being forwarded.
> 
> I see two options:
> 
> 1) always transmit ALIGN primitives when there are no Forward 
> Dword indications, or
> 2) if a data frame is currently being forwarded, transmit 
> ALIGN primitives when there are no Forward Dword 
> indications, otherwise transmit idle dwords.
> 
> The second option would obviously require the expander to 
> have the intelligence to know that data frames 
> are being forwarded.
> 
> Are there any potential drawbacks with either option?
> 
> Thanks,
> 
> Fred Dutton
> ----------------------------------------------------
> Fred Dutton * QLogic * 949.389.6340
> 
> 
> 
> 
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